Not an expert in macroeconomics either, but in a perfect free market there shouldn't be a lot of difference between renting and buying: if you can get a 5% yearly return by renting out a house, then the person renting from you can probably also get a 5% yearly return by investing their freed-up capital elsewhere and/or by not having to pay interest. If renting is too expensive, you buy, and if buying is too expensive, you rent. If one kind of investment like land or housing turns out to be particularly lucrative, capital will flow towards that type of investment and drive down returns towards the average again. Companies rent and lease stuff all the time, even if they have the money to buy, because often it just makes more sense. So there has to be
something to disturb that happy picture and benefit owners at the expense of renters: a wonky tax structure, speculation, rate of return on land consistently higher than for other asset classes, cultural norms that value homeownership, who knows. Ownership of multiple dwellings by the wealthy might play a role, but in itself it's not a sufficient condition for high housing prices.
(It would be different if the wealthy were buying these houses to live in them or to leave them empty, as that would increase demand and constrain supply. Happening in London, Vancouver and a bunch of other places, I think. Also sort of like what happened with the quinoa fad: https://en.wikipedia.org/wiki/Quinoa#Effects_of_rising_deman...)